Sentencing them, the judge said it was "a terrible crime which has few parallels in modern criminal history".
The killers were 14 at the time, apparently making them Britain's youngest double-murderers.
The judge at Nottingham Crown Court, Mr Justice Haddon-Cave, said the case had "defining and particularly chilling" features and condemned their conduct as "grotesque".
Jurors heard that the killers went on to share a bath, have sex, and watch four Twilight vampire films after the murders in Dawson Avenue, Spalding.
Addressing the teenagers, the judge told them: "There is a clear intention to kill both victims - both defendants admitted wanting to murder them.
"There was remarkable premeditation and planning - it was, on any view, substantial, meticulous and repeated."
He added: "The killings were brutal in the form of executions, and both victims, particularly Elizabeth Edwards, must have suffered terribly in the last minutes of their lives."
Mrs Edwards and her daughter were repeatedly stabbed by the couple, who were described in court as having a Bonnie and Clyde-style relationship, on 13 April.
'Most distressing and disturbing case'
Mrs Edwards was stabbed by the boy eight times, twice in the throat, in a deliberate attempt to ensure her daughter was not woken by screams or cries for help.
Katie was stabbed twice in the neck with severe force before she was smothered by the boy.
During his sentencing remarks, the judge said both teenagers were equally responsible for the murders and had "revelled in what you achieved".
"I see no reason to distinguish between you in any way," he said.
Outside court, Karen Thompson, deputy chief crown prosecutor for the East Midlands, said: "This is one of the most distressing and disturbing cases that I have ever encountered.
"Our deepest sympathies are now with the extended family and friends of Elizabeth and Katie Edwards as they attempt to come to terms with this horrific crime."
BBC.
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